The New Physics and Its Evolution eBook

In the case of sound vibrations, on the other hand,
it should be noted that experiment, consistently with
the theory, proves that the speed increases with the
amplitude, or, if you will, with the intensity.
M. Violle has published an important series of experiments
on the speed of propagation of very condensed waves,
on the deformations of these waves, and on the relations
of the speed and the pressure, which verify in a remarkable
manner the results foreshadowed by the already old
calculations of Riemann, repeated later by Hugoniot.
If, on the contrary, the amplitude is sufficiently
small, there exists a speed limit which is the same
in a large pipe and in free air. By some beautiful
experiments, MM. Violle and Vautier have clearly
shown that any disturbance in the air melts somewhat
quickly into a single wave of given form, which is
propagated to a distance, while gradually becoming
weaker and showing a constant speed which differs little
in dry air at 0 deg. C. from 331.36 metres per
second. In a narrow pipe the influence of the
walls makes itself felt and produces various effects,
in particular a kind of dispersion in space of the
harmonics of the sound. This phenomenon, according
to M. Brillouin, is perfectly explicable by a theory
similar to the theory of gratings.

CHAPTER III

PRINCIPLES

Sec. 1. THE PRINCIPLES OF PHYSICS

Facts conscientiously observed lead by induction to
the enunciation of a certain number of laws or general
hypotheses which are the principles already referred
to. These principal hypotheses are, in the eyes
of a physicist, legitimate generalizations, the consequences
of which we shall be able at once to check by the
experiments from which they issue.

Among the principles almost universally adopted until
lately figure prominently those of mechanics—­such
as the principle of relativity, and the principle
of the equality of action and reaction. We will
not detail nor discuss them here, but later on we
shall have an opportunity of pointing out how recent
theories on the phenomena of electricity have shaken
the confidence of physicists in them and have led
certain scholars to doubt their absolute value.

The principle of Lavoisier, or principle of the conservation
of mass, presents itself under two different aspects
according to whether mass is looked upon as the coefficient
of the inertia of matter or as the factor which intervenes
in the phenomena of universal attraction, and particularly
in gravitation. We shall see when we treat of
these theories, how we have been led to suppose that
inertia depended on velocity and even on direction.
If this conception were exact, the principle of the
invariability of mass would naturally be destroyed.
Considered as a factor of attraction, is mass really
indestructible?